Driving behavior has been identified as a major contributing factor to critical accidents and road crashes. In Hong Kong, most road crashes (78.58%) involving traffic casualties are considered to be the drivers’ fault. A driving simulator approach was thus used to investigate driver behavior in distracted driving scenarios and scenarios involving signal countdown displays (SCD) at junctions. Distracted driving is considered to be one of the most common causes of traffic crashes. Two distraction experiments of driving while distracted by texting messages and using hands-free mobile phones were conducted. In the experiment on reading and typing text messages, the drivers’ reaction time (RT), driving lane undulation (DLU), driving speed fluctuation (DSF), and car-following distance (CFD) between the test and leading cars were analyzed according to the following conditions: (1) no distraction, (2) reading and typing Chinese text messages and (3) reading and typing English text messages. The results indicated that reading and typing text messages while driving should be prohibited regardless of whether Chinese or English is used, as they cause remarkable impairments in driving performance. In the experiment on hands-free mobile phone use, the drivers’ RT, DSF, car-following distance undulation (CDU), and car-following time headway undulation (CTU) were used to measure and compare driving performance under the distraction conditions of no distraction (ND), normal conversation (NC), and seven levels of mathematical calculation tasks. The causal relationship between the calculation levels and driving performance factors were also investigated using a structural equation model (SEM). The study revealed that normal conversation on a hands-free mobile phone impaired driving performance to a degree equivalent to the distraction caused by level 3 mathematical calculations. In addition, the seven levels of calculation tasks can be applied to measure the distraction effects of other driving behaviors. Road junctions and ...